Water tank cover



FIG. 1 is a top view of a water tank cover showing my new ornamental design;

FIG. 2 is a side view of the water tank cover of FIG. 1;

FIG. 3 is a bottom view thereof;

FIG. 4 is a frontal elevation of the top side of a single section of my new ornamental device; and,

FIG. 5 is a rear elevation thereof. 

The ornamental design for a water tank cover, as shown and described. 